To Have And To Hold
by OrtonsMistress
Summary: Derek Shepard's baby sister comes to Seattle looking for help. What happens when she ends up falling in love with his best friend? Will it be easy? Or will Derek's over-protective nature keep Allison from being happy? *Story DISCONTINUED*
1. Chapter 1

Prologue

Disclaimer: I don't own any Grey's characters. They are all owned by Shonda Rhimes. The only person I own is Allison Shepard and that is it.

A/N: This is my first attempt at a Grey's Anatomy fic. I only started watching at the beginning of last season, and I'm now catching up with it on Lifetime. I know a lot of you may not like Mark being with an OC, but for some reason I just can't write a Mark/Lexie fic, even though I loved them together on the show. While this isn't much of a chapter, I just wanted to start out with something a little different. Chapter 1 will show when Allison first arrived in Seattle and it will progress from there.

"He's not coming is he?" Allison asked, looking around at her mom and sisters.

"He'll be here sweetie. He wouldn't miss this for anything." Carolyn said, trying to calm her youngest daughter's nerves.

"Mom, he was never really thrilled about Mark and I being together." She said softly. "Why should I believe that he would be here to walk me down the aisle to marry him?"

Not getting an answer from her mom, she heard the door open to the room, and turned around and tears sprung into her eyes, when she saw her brother standing there. "I wouldn't miss this for anything in the world Allie." Derek said, walking over to her. "I'm sorry for being such an ass about you guys. You both deserve to be happy, and if it's with each other, who am I to stand in the way."

"I love you Bubba." She said, throwing her arms around his neck and hugging him tightly. "You have no idea how much this means to me. Now I don't feel like you'd hate me if I went through with the wedding."

"Girls, why don't we give your sister and brother a few minutes alone." Carolyn said, herding her other daughters out of the room.

"I don't know why it's so hard for me to see you so grown up." Derek said softly, shaking his head at the sight of his little sister in her wedding gown.

"Cause I'm the baby of the family and it's hard for you to accept that I'm grown up now?" She asked teasingly, although she'd heard a lot of that the last few months while planning her wedding.

"That and it's hard to accept that I'm the one that has to give you away." He said. "It's harder for me to do that, than it was for me to walk the others down the aisle."

"You know Der, you're always going to be important to me." She said honestly, looking him in the eye before continuing. "Who else can I go to, when Mark is driving me crazy about something stupid? Who can I go to when I'm freaked out being alone at the house, while he's working late?"

"I'm really sorry for everything Allie." He whispered, pulling her into a hug. "I'm sorry that I wasn't there for you more, after your attack and all." He finished, knowing there were plenty of nights when she snuck into the O.R gallery while Mark would be doing a surgery, just so she wouldn't have to sit at home alone and be afraid of Frankie and his friends breaking in and hurting her.

"Derek, I know you sat in the hospital room for days before I woke up." Allie said, smiling at him softly. "I could smell your cologne and Meredith and mom told me you refused to leave my side the first few days. You wouldn't listen to Bailey or the chief when they said you couldn't work my case."

"Well I didn't trust you to Shadow Shepard. I wanted to make sure that you were getting….." He started, when Allie cut him off.

"I love you too Derek." She said, smiling up at him.

Looking down at her with a smile, Derek had to fight back the tears in his eyes. "You look beautiful today." He whispered, clearing his throat of any ensuing tears.

"You ready to walk me down the aisle now?" She asked, opting not to tease him about the tears.

"No, but I guess I have to be." He replied, leaning down and kissing her cheek gently. "Let's go."

Grabbing her bouquet, Allie looped her arm through Derek's and let him lead her out of the room and to the back of the church. Standing there she thought back on how far she had come, since she first arrived in Seattle a year and a half before. The reason behind her coming and the hell on Earth she endured once her secret past caught up with her there. Taking a deep breath, she smiled up at her older brother, protector and best friend, one more time, before the doors opened and he walked her down the aisle and gave her away to his best friend and someone he considered a brother. Both had mixed emotions running through them on this day, one ready to let go of the past, while another had a hard time letting go.

As the wedding march started playing, the doors opened to reveal Allison standing there on her brother's arm, waiting to be led down to the man of her dreams, Mark Sloan. Letting out a deep breath, she started down the aisle, a watery smile on her face, as she realized that all her dreams were starting to come true.


	2. Chapter 2

A/N: This chapter is starting out when Allison first arrives in Seattle. I'm going to show the building of the relationships, leading up to what was seen in the Prologue.

Chapter 1

"Good Lord, who do you have to know to get a map of this damn place?" Allison Shepard asked, leaning against the opened office door.

"Allie, what are you doing out here?" Derek asked, going over and scooping his baby sister up in his arms.

"Can't a little sister visit her favorite brother?" She asked, smiling at him cutely.

"Allie, I'm your only brother, and that cutesy smile thing doesn't work anymore." He said, setting her back on her feet.

"So where's this wife of yours that I have yet to meet?" She asked. "I hope she's better than Addison. I hated when I was little, she thought I should be happy our names were close sounding. Psh, I almost begged mom to change my name."

"Meredith is on rounds right now. You can meet her later. Now why are you really out here?" He asked, giving her a look that said spill it.

* * *

Almost twenty minutes later, Allison had finished telling Derek everything about what brought her clear across the country to see him.

"I know you probably hate me now." She said softly, looking down at her feet.

"How much Allison?" Derek asked, letting her know then that he wasn't too happy with her, when he used her full name.

"$250,000." She answered quietly, too scared to move.

"How could you let yourself get in this deep kid?" He questioned, running a hand over his face.

"I don't know, it was like before I knew it, I had to pay all this money. I've lost everything Derek, my house, my car, my job." She said honestly. "I don't know how to get out. Mom bought my plane ticket out here, she didn't trust me with her credit card. Can't really say that I blame her."

"Listen, I need to talk this over with Meredith, we'll see about getting you set up in my old trailer. Then when I can get some time off from here, you and I will fly back to New York and pay this off." Derek said, going over and pulling her into a hug.

"Thank you Derek! I swear I will get a job out here and pay you back." She said, hugging him tightly.

"Yeah, you definitely will." He said, as someone knocked on the door then.

"Chief, the hospitals lawyer is here to speak to you." A nurse said, opening the door a bit.

"Go on Derek, I'll just catch up with you later. Call me whenever you get off." Allison said, smiling faintly.

"Okay." He said, kissing the top of her head. "Love you kid."

"Love you too." She replied, before making her way out of his office.

* * *

"Who's that girl that just walked out of Derek's office?" Meredith asked, as she was heading to his office with Mark.

"That's Allison Shepard. Derek's baby sister." Mark replied, getting a good look at her.

"Wonder what she's doing out here." She mused, missing the look on Mark's face.

"Don't know." He replied, as Allie turned around and saw him.

"Mark!" She exclaimed, running toward him and jumping up into his arms. "I've missed your man-whore ass."

"Allie, it's great to see you too." He said, chuckling lightly. "You've grown up on me."

"Yeah, well that's what happens when you reach twenty-seven. I'm not the same little girl that used to follow you and Derek around." She said, smirking at him.

Watching them interact, Meredith couldn't help but wonder if Mark was as attracted to the youngest Shepard, as she obviously was to him.

"Ehm." Meredith cleared her throat, getting Mark's attention.

"Oh, Mer meet your sister in law, Allison Shepard." He said, not taking his eyes off of Allie. "Allie, meet Meredith."

"It's nice to finally meet you." Allie said, turning her attention to Meredith then. "I can already tell you're better for my brother than the evil witch, Addison."

"Thank you." Meredith replied, chuckling lightly.

"Anyway, I was about ready to go get some lunch. Do you guys want to come? Meredith, I would love to get to know you better." Allie said, looking back and forth between the two of them.

"You guys can go. I'm on Bailey's post ops." Meredith said, knowing that her young sister in law, had a slight crush on 'McSteamy'.

"Great, gives us a chance to catch up. Plus I don't know where anything is around here." Allie said, smiling up at Mark. "Meredith, I look forward to getting to know you better."

"Likewise." Meredith said, as Allie and Mark headed toward the elevator to leave.

* * *

A few hours later, Mark and Allie were still sitting at Joe's catching up, when Mark's phone rang.

"Yeah." He said, rolling his eyes a bit when Derek started talking.

"You better not be trying anything with my little Sloan." Derek threatened, not wanting her to get taken advantage of, or to just be used as one of Mark's play things. He'd seen it happen to a lot of women before, and he didn't want Allie to become a statistic.

"Okay dad." Mark retorted sarcastically. "We're just sitting at Joe's, playing pool and catching up."

"Alright, well do you mind taking her back to her hotel, then out to the trailer? I'm not getting out of here till late." Derek asked, knowing Mark was off the next day, and would most likely not have a problem keeping Allie company.

"Yeah sure, no problem." He replied, before asking. "Is the power even turned on out there anymore?"

"Damn it, no." Derek said, having had it turned off recently.

"Look, I'll just take her back to my apartment, tomorrow you call and get the power back at the trailer." Mark suggested, as Allie was running the pool table pretty much.

"Alright, I'm serious Mark, don't try anything." He threatened, looking over some paperwork.

"Goodbye." Mark said, hanging up on him.

"Let me guess, big brother doesn't want you to do this to me." Allie said, turning Mark around and kissing him lightly. The six beers and three shots of tequila making her bolder than she normally was.

"Allie, what are you doing?" Mark asked, once he pulled away from the kiss.

"Something I've wanted to do since I was twelve." She replied, looking up at him.

"Let's get out of here." He said, throwing some money down, and pulling her out of the bar.

* * *

By the time they got back to Mark's apartment, Allie's drunken haze was fading, though she wasn't going to let Mark know.

"Allie, you realize we can't do this, right?" Mark asked, knowing Derek would kill him if he ever found out, and make it look like an accident.

"Why not Mark?" She asked, standing with her hands on her hips. "I'm not a little girl anymore."

"Yeah, but you're like a little sister to me. Derek would kill me if he ever found out." Mark said, trying to talk some sense into her.

"Are you really going to tell Derek you had sex with his baby sister?" She asked, taking her shirt off.

"No, because I'm not going to." He replied, handing her back her shirt.

"Seriously Mark, when have you ever listened to anything Derek has told you?" She questioned, walking up to him, tossing her shirt off to the side. "You did after all sleep with his first wife."

Grabbing her around the waist, Mark lifted her up to meet his eyes. "Allison, we can not do this." He said, trying to resist his desire to have his way with her.

"Mark, you've slept with Nancy and Kathleen before. Don't try to say you can't sleep with me cause it'd be weird." She told him, as she wrapped her legs around his waist.

"Allie, you're drunk and you don't know what you're asking here. Things could get really weird between us." He replied, as that was the last thing he wanted. "Sleeping with you would be a lot different than me being with Nancy or Kathleen."

"Mark look, I've wanted you ever since I was fifteen and lost my virginity to Jake Finster in his pool." She said, getting down from his arms. "I know I probably shouldn't have, but with every guy I've ever been with, I would always imagine I was with you. Growing up with older sisters, I'd always have to hear about their dates, or anybody they slept with. I always kind of held you in that regard. I mean, I know I used to call you things like man-whore and stuff, but I figured you would always see me as a little kid, that tagged along with you and Derek everywhere." She finished, looking down at her feet.

"I never knew you felt like that." Mark said, as another part of his anatomy was starting to win in his thinking. "Allie, are you really sure this is what you want? Once we do this, there's no taking it back."

"Mark I've told you, I want this. I want you, I always have." She said, walking over and running her hands up inside his shirt.

"Okay." He mumbled, before crashing their lips together, as they quickly started pulling clothes off each other their hearts pounding, as Mark picked her up and carried her into his bedroom, where they made love the rest of the night.


End file.
